1. Field of the Invention
This invention relates to a nonvolatile semiconductor memory device in which a channel film made of silicon is formed on an insulating film, and a method for manufacturing the same.
2. Background Art
Recently, as an alternative to the planar nonvolatile semiconductor memory device, a nonvolatile semiconductor memory device in which a plurality of MONOS (metal-oxide-nitride-oxide-silicon) type memory cells are three-dimensionally stacked has been developed (see, e.g., JP-A-2008-171918(Kokai)). This nonvolatile semiconductor memory device is manufactured as follows. Gate electrodes and interlayer insulating films are alternately formed on a substrate to form a stacked body, and a through hole extending in the stacking direction of the stacked body is formed therein. A charge block film, a charge storage film, and a tunnel insulating film are formed in this order on the inner surface of the through hole. Subsequently, silicon is deposited by the CVD (chemical vapor deposition) process, for instance. Thus, a vertically extending silicon pillar is buried in the through hole, and serves as a channel of memory cells.
However, in this manufacturing method, the silicon pillar is formed by depositing silicon on the tunnel insulating film. Hence, microscopic structural defects at the atomic level are generated at high density at the interface between the tunnel insulating film and the silicon pillar, and this structural defect forms an interface state or a fixed charge. This decreases the operating speed of the cell transistor constituting the memory cell. Furthermore, the threshold voltage of the cell transistor varies after prolonged operation and causes malfunctions.